The invention relates to improvements in apparatus for testing visual functions of human eyes, and more particularly to improvements in apparatus which employ so-called perimeters.
The testing of visual functions embraces perimetry, determination of sharpness of visual perception on the retina, determination of flicker frequency, determination of contrast sensitivity and color contrast sensitivity and many others. Apparatus which can carry out such tests are called automatic perimeters and are available for many years. As a rule, the eye to be examined is moved to a position at or close to the center of a hollow hemisphere known as cupola. The eye which is moved to such position is supposed to be directed toward the apex of the cupola, and more particularly toward the apex of the hemispherical internal surface of the cupola. A projector is employed to present stimuli at selected points of the internal surface of the cupola, and the patient or subject is supposed to generate signals in response to detection or non-detection of stimuli.
A drawback of presently known perimeters is that they are bulky and expensive. As a rule, the diameter of a cupola is in the range of 60-100 cm. The center of the cupola is normally located at the eye level of a subject who is seated during examination. Therefore, the overall height of an automatic perimeter is necessarily in the range of two meters. This is the reason that automatic perimeters are normally found only in hospitals and in establishments (employing or owned by ophthalmologists) which specialize in the detection and treatment of diseases and defects of human eyes. Such rather bulky and highly expensive automatic perimeters are much less likely to be found in the offices of individual eye doctors or opticians who are not likely to invest substantial sums of money and whose offices are not likely to have the required space for an instrument which might not be used as frequently as in a highly specialized establishment.